Line pulse modulator for multichannel transmitters



Sept. 14, 1948.

PULSES P. C. BETTLER ETAL LINE PULSE MODULATOR FOR MULTICHANNEL TRANSMITTERS Filed Feb. 3, 1945 ANTENNA ANTENNA ANTENNA INVENTOR. HOWARD D. DOOLTTTLE PHILIP C. BETTLER BY Wig A1 ATTORNEY Patented Sept. 14, 1948 LINE PULSE MODULATOR FOR MULTI- CHANNEL TRANSMITTERS Philip C. Bettler, Boston, and Howard D. Doolittle,

Cambridge, Mass, asslgnors, by mesne assignments, to the Government of the United States of America as represented by the Secretary of War Application February 3, 1945, Serial No. 576,114

The present invention relates to radar objectdetection systems, and more particularly to a circuit arrangement for simultaneously operating a plurality of high-frequency wave generators in a radar system. i

In certain pulse-echo object-detection systems entailing the use of two or more antennas, it is required that more than one magnetron operating from the same pulse modulator be employed. While all the magnetrons are synchronized to transmit pulses in coincidence, they do not necessarily have the same impedance, especially when the magnetrons are adapted to operate at different frequencies. l

Accordingly, it is an object of this invention to provide a single line pulse modulator for energizing a plurality of transmitters having difierent impedances, the energization of all transmitters being simultaneous.

An additional object of this invention is to provide a single line pulse modulator for energizing a plurality of parallelly connected radar transmitters having different impedances and different operating frequencies, the modulator simultaneously energizing all transmitter-s preferably for equal lengths of time and capable of furnishing any desired preselected power distribution among the transmitters.

For a better understanding of the present invention, as Well as other features thereof, reference is had to the following description to be read in connection with the accompanying drawing schematically showing a preferred embodiment of a radar transmitter in accordance with the invention.

A plurality of magnetrons If H, l2 and :3 are provided energized from a direct-current power source applied between terminal I l and ground. The oscillations yielded by each magnetron are fed to separate antennas. Terminal M is connected through a choke coil l5 and a pulse-forming line It to one end of the primary winding of a pulse step-up transformer H, the other end thereof being grounded. The secondary winding of transformer ll is connected to the electrodes of magnetron iii. In a like manner, magnetron i I is coupled to the power source through a pulse transformer l8 and a pulse-forming line l9, magnetron i2 is coupled to the power source through a pulse transformer 29 and a pulseforming line 2|, and magnetron I3 is coupled to the power source through a pulse transformer 22 and. a, pulse-forming line 23. The characteristic impedance of each connected pulse-forming line and associated transformer and switch 24 is made 4 Claims. (Cl. 250-17) equal to the impedance of the magnetron associated therewith. Stated differently the impedance of transformer l1 and the impedance of modulator switch 24 match the impedance of line IS, the

matching being necessary to avoid. any wave re-' pulse-forming line is made equal to the impedance of its associated magnetron and switch 24.

A modulator switch 24 is connected between ground and the junction of choke l5 and pulseforming line It, said switch being of any suitable construction, as for example, that of the fixed or rotary. spark gap type, or of the thyratronlty'pe. Each of the pulse-forming lines l6, l9, 2| and 23-, which may be either of the Guillemin line type (as shown), or the ordinary artificial transmission line, is charged through choke l5 and the primary winding of its associated transformer. The inductance of choke l5 and the capacitance of the line form a resonant circuit so that the voltage across the line tends to oscillate. At the peak of the first positive swing, the line is charged to a voltage considerably higher than the D.-C. supply voltage. At this instant, a, triggering pulse is applied by a source 25 to modulator switch 24 rendering it conductive, thereby discharging each of pulse-forming lines l6, I9, 2| and 23 through its associated transformer primary winding and applying concurrent surges of energy to magnetrons Iii, ll, l2 and I3.

As seen in the drawing, only one modulator switch .24, is employed which insures that the pulses w ll be simultaneous. and since the charging condensers in each of pulse-forming lines it, iii, 2! and 23 assume the same potential, the energy delivered to each of the loads is the same. the power to the magnetrons I8, I I, I2 and it will be divided evenly or in certain proportions if so desired, the latter being accomplished by adjusting the parameters of the individual lines. Another advantage of this arrangement resides in the fact that the storage capacitors of the pulse-forming lines, being charged in parallel, need be subjected only to the voltage required for one magnetron, thereby giving an extended life to the pulse-forming lines or permitting a less expensive construction. It is to be noted that the amplitude of the peak current across modulat-or switch 24 is materially increased, hence it must be constructed. with this factor in mind.

While there has been described what is at present considered a preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a multi-channel pulse transmitter, a plurality of magnetrons, a corresponding plurality of pulse-forming networks, each of said networks being coupled to its respective magnetron, means for charging in parallel said'plurality of networks, and means for periodically and simultaneously discharging said plurality of networks to deliver a pulse of energy from the respective network to the magnetron coupled to said network.

2. A multi-channel transmitter including a plurality of transmitters, a corresponding plurality of artificial lines, a like plurality of coupling means, one terminal of each line being coupled to its respective transmitter through the corre sponding coupling means, a source of direct current potential, a choke coil connected with one end to one terminal of said source and with the other end to the remaining terminals of said artificial lines, a connection between the other terminal of said source and all of said coupling means, whereby said source is capable of simultaneously charging all of said artificial lines, a single modulator switch shunting all of said lines and all of said coupling means, and a source of periodic pulses connected to said switch for Deriodically closing said switch, whereby all of said lines are simultaneously discharged through said switch and through the respective coupling means.

3. A multi-channel pulse transmitter as defined in claim 2 in which the parameters of said artificial lines, switch and coupling means are made to produce reflectionless discharges of said lines.

4, In a multi-channel transmitter capable of transmitting simultaneously a plurality of pulses of equal duration and substantially equal power, a plurality of parallelly connected transmitting channels, a corresponding plurality of pulse- Iorming networks having equal capacities, a corresponding plurality of means for coupling each of said networks to its respective channel, a source of charging potential in parallel connection with said plurality of networks and said means, and a single modulator switch common to all of said networks and said coupling means, said switch Deriodically and simultaneously discharging said plurality of networks through said means.

PHILIP C. BETTLER. HOWARD D. DOOLITTLE.

REFERENCES CITED The following references are of record in the file of this patent:

UNI'I'ED STATES PATENTS Number Name Date 2,041,830 Hansell May 26, 1936 2,103,362 Hansell Dec. 28, 1937 2,227,513 Roosenstein et a1. Jan. 7, 1941 2,231,591 Pieplow Feb. 11, 1941 2,265,825 Urtel eta1 Dec. 9, 1941 2,276,994 Milinowski, Jr Mar. 17, 1942 2,415,116 Stiefel Feb. 4, 1947 2,420,309 Goodall May 13, 1947 

